linux-kernel - Re: PCI-ISA Bridge not operating

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Date:	Fri, 11 Jul 2008 16:31:33 -0400
From:	David Brigada <brigad@....edu>
To:	unlisted-recipients:; (no To-header on input)
CC:	Jordan Crouse <jordan.crouse@....com>, jim.cromie@...il.com,
	LKML <linux-kernel@...r.kernel.org>,
	linux-geode@...ts.infradead.org
Subject: Re: PCI-ISA Bridge not operating

Jordan Crouse wrote:
> On 11/07/08 16:14 -0400, David Brigada wrote:
>> Jordan Crouse wrote:
>>> On 11/07/08 14:58 -0400, David Brigada wrote:
>>>> David Brigada wrote:
>>>>> Jordan Crouse wrote:
>>>>>> On 11/07/08 10:58 -0400, David Brigada wrote:
>>>>>>> Hi,
>>>>>>>
>>>>>>> I'm working with the MSM800XEV board from Digital-Logic.  This board 
>>>>>>> uses a Geode LX800 for a CPU and has the CS5536 companion board also 
>>>>>>> installed.  The board works with an IT8888G IC that provides a PCI/ISA 
>>>>>>> bridge to a PC/104 bus that is externally provided.
>>>>>>>
>>>>>>> If I boot with FreeDOS, I can twiddle I/O ports, and the proper ISA 
>>>>>>> signaling comes over the PC/104 bus.  In Linux, the /IOW or /IOR line 
>>>>>>> goes low as expected, but the address doesn't come over the bus.  The 
>>>>>>> DOS that I'm running doesn't seem to have any specific drivers for the 
>>>>>>> chip, I'm guessing that the hardware should "just work" --- the IT8888G 
>>>>>>> is designed to grab I/O requests in the ISA range off the PCI bus after 
>>>>>>> a short delay if nothing else grabs them first.
>>>>>>>
>>>>>>> I have a feeling that it has something to do with the CS5536 companion 
>>>>>>> chip, as it seems as though there is a driver for a PCI/ISA bridge on 
>>>>>>> that chip, though I can't get much detail from AMD's datasheet on that 
>>>>>>> functionality.  I do know that on the MSM800XEV, any such functionality 
>>>>>>> is wired to the IT8888G, not the CS5536.
>>>>>>>
>>>>>>> There are two kernel config options related to the PCI IDs of the parts 
>>>>>>> of the device that handle the ISA bus, CONFIG_SCx200_ACB and 
>>>>>>> CONFIG_CS5535_GPIO.  I've tried disabling both, but it doesn't seem to help.
>>>>>>>
>>>>>>> In lspci, the CS5536 PCI/ISA bridge is shown, but not the IT8888G.
>>>>>>>
>>>>>>> Any ideas?
>>>>>> ISA should indeed "just work".  The only thing I'm wondering is if
>>>>>> the kernel is interfering (it shouldn't).  I assume that since it works
>>>>>> in FreeDOS that there is no possibility that something on the PCI bus
>>>>>> is grabbing the cycles instead.
>>>>> That's what I'm thinking --- that the CS5536 PCI/ISA bridge is claiming 
>>>>> the cycles.
>>>>>
>>>>>> How are you trying to access the device in Linux?  Through a kernel module
>>>>>> or a user application running as root?
>>>>> I've tried both.  I have a kernel module that I wrote for the hardware. 
>>>>>   When I couldn't get that working, I tried looping some code that keeps 
>>>>> touching the same I/O port that I'm using.
>>>>>
>>>>>> Jordan
>>>>>>
>>>>> Dave
>>>> Looking through the documentation for the CS5536, in the "CS56536 
>>>> Companion Device Data Book," section 5.2.8, it says the following:
>>>>
>>>>  > If the SDOFF (Subtractive Decode Off) bit in the GLPCI_MSR_CTRL (MSR
>>>>  > 51000010h[10]) is cleared (reset value), any PCI transaction, other
>>>>  > than Configuration Read/Write, Interrupt Acknowledge, and Special
>>>>  > Cycle transactions, not claimed by any device (i.3., not asserting
>>>>  > DEVSEL#) within the default active decode cycles (three cycles
>>>>  > immediately after FRAME# being asserted) will be accepted by GLPCI_SB
>>>>  > at the fourth clock edge.
>>>>
>>>> This is the same behavior that the IT8888G chip uses --- it waits three 
>>>> cycles for another device to claim it and then passes the transaction 
>>>> along.  I'm guessing that the CS5536 might be grabbing it (maybe it's 
>>>> electrically closer, or the logic is more optimized) before the IT8888G 
>>>> can handle it.
>>>>
>>>> Does this seem feasible as to what could be happening?
>>> Sure, but then why does FreeDOS work?  It shouldn't be any different
>>> when the bits hit the line.
>>>
>>> Jordan
>> That *is* puzzling.  When I do lspci, the entry for the IT8888G does not 
>> appear.  I don't have much experience with PCI internals.  Would that be 
>> because there is no driver for it in the kernel, or is there something 
>> more insidious afoot?
> 
> Well - the first step would be to get a dmesg output.  if the kernel
> is doing anything to the device at all, the dmesg will show it.
> 
> Jordan
> 

[Sorry, Jordan about the double-mail]

The dmesg output doesn't have anything related to the device.  I have 
attached my dmesg output for completeness.  Ignore the last four lines, 
that's my testing.  The PCI ID of the IT8888G is 1283:8888.

Dave

View attachment "dmesg-out" of type "text/plain" (10590 bytes)